This invention deals generally with heat exchangers and more specifically with a compact fluid to fluid heat exchanger.
Typical heat exchangers use thermal conduction through metal structures with a structure exposed to heat from a fluid on one side of a surface and with a cooling fluid on the other side of the surface.
Cooling a high power density heat exchanger surface, that is, a surface through which intense heat is being transferred, is a particularly difficult problem. If the heat is delivered to a heat exchanger surface in multiple locations, or generally across the entire surface, the heat removal must similarly be over the entire surface. In the simplest configurations, such as with liquids flowing through cooling pipes attached to the opposite sides of a heat exchanger plate, just the thermal resistance through the heat exchanger plate, between the heat input fluid and the heat removal fluid, can permit the temperature of the hotter fluid to rise too high.
Even with the use of evaporation on the cooler side it is difficult to accomplish a small temperature difference in such a heat exchanger. One reason is that high heat input at one location can create a high vapor pressure at that point and prevent additional liquid from reaching that location for generation of additional cooling vapor. Such a situation can lead to failure of the heat exchange action.
Although there have been some approaches to cooling a heated surface without the use of evaporation, they also have not proven entirely satisfactory. U.S. Pat. No. 5,727,618 by Mundinger et al suggests one typical approach for cooling a high power density surface of a laser diode array. That patent discloses channels in a solid plate adjacent to the heated surface. U.S. Pat. No. 5,205,353 by Willemsen et al discloses alternating complimentary wedge shaped channels formed in a porous layer, with fluid fed into every other channel and out the channels between the input channels.
Such channeled designs suffer from several shortcomings. Those with solid channels such as Mundinger et al are easier to manufacture, but only directly cool the portions of the heated surface in contact with the fluid channels. The balance of the heated surface must conduct heat through the heated structure to reach the portions in contact with the fluid in the same manner as is required for attached pipes.
Those designs such as Willemsen et al, which have channels in porous materials, are difficult and expensive to manufacture. Furthermore, they only supply a limited quantity of additional fluid in contact with the heated surface. They only add the cooling fluid flowing through the portion of the porous layer in direct contact with the heated surface to the amount which would be supplied by channels in adjacent solid material. Fluid passing through the porous material only a small distance removed from the heated surface adds little to the heat transfer from the heated surface.
It would be very advantageous to have a heat exchanger which supplies heated and cooled fluid to the entire surface on both sides of the heat transfer structure and yet was simple to manufacture.
The invention is an easily assembled heat exchanger using an internal porous metal pad. The heat exchanger is constructed of two halves each with only four simple parts. Each half includes a cup shaped casing, a pad of sintered porous metal, a manifold block with channels, and a lid. Each lid includes input and output fluid holes which are connected to sets of alternating channels in the manifold block, so that adjacent channels are isolated from each other and are connected to only either the input or the output holes. Thus, the only access between the adjacent input and output channels is through the sintered metal wick which is sandwiched between the manifold block and the bottom of the casing. Fluid flow through the wick thereby affects the bottom of the casing which is held in heat conducting contact with an exact duplicate half so that heat transfer occurs between the liquids flowing in both halves. Another embodiment simply uses a single bottom piece with the two halves attached to opposite surfaces of the bottom.